With the advent of an industrial society, people are exposed to noise pollution at greater and greater levels; both from background, such as street traffic, airplanes, construction sites and intentional exposure to high sound levels such as cell phones, MP3 players, and rock concerts. Studies show that ear damage, leading to permanent hearing impairment is not only increasing in the general population, but increasing at a significantly faster rate in younger populations.
The potential for hearing damage is a function of both the loudness and the duration of exposure to the sound stimulus. Safe listening durations at various loudness levels are known, and can be calculated by averaging audio output levels over time to yield a time-weighted average. Standard guidelines published by OSHA, NIOSH or other agencies are known. This calculation can be even further improved by or counting for aspects of the playback scenario, specifically the characteristics of the sound source and their proximity to the listener's ear.
Studies have also indicated that hearing damage is a cumulative phenomenon. Although hearing damage due to industrial or background noise exposure is more thoroughly understood, the risk of exposing one's self to excessive noise, especially with the use of headphones has also been recently studied. Protecting the ear from ambient noise is primarily done with the use of static earplugs that attempt to shield the inner ear from excessively high decibel noise. Background noise canceling earphones such as those produced by Bose and others, attempt to protect the ear form excessive ambient noise by producing a counter noise wave to cancel out the ambient noise at the ear. These prior art devices have been less than satisfactory because they do not completely prevent high decibel noise from reaching the ear, and do not account for the duration of exposure to harmful sounds at the ear.
It is also known from the prior art to provide active noise reduction at the ear to protect the ear from exposure to loud noises as disclosed in U.S. patent Application No. US2005/0254665. The art actively attenuating noise reaching the inner ear utilizing a control; a connection with an earpiece and attenuating the noise to the ear. However, there is no monitoring of the noise over time to account for the cumulative effect. Furthermore, there is no accounting for any restorative effects for sound pressure levels which are healing to the ear rather than destructive.
Dosimeters, such as that described in U.S. published Application No. US2005/0254667 are known. The device periodically measures prior sound level within the ear canal. However, the device does not take into account the cumulative effect of the noise or the effect of any restorative period. Furthermore, no remedial action is taken as a result of the readings.
It is also known from the prior art that headphones for consumer electronics have been provided with a predetermined maximum output level in an attempt to prevent ear damage. This approach is ineffective as it does not take into account listening duration and the calculation of risk for auditory injury. Other headphones are maximum-limited to produce levels that can still result in significant overexposure given enough time, or limit the user to levels, which may not be sufficient to achieve a short term listening level. In the latter case, consumer acceptance for the protective gear could be severely limited and a product would fail to survive in a competitive market and therefore be of no use.
Another alternative known in the art is to reduce the headphone output levels by increasing earphone impedance via an accessory placed between the media player and the earphones. The limitation of this approach is that it gives no consideration to the duration of exposure, and again either the user's chosen listening level cannot be achieved because the maximum level is too limited, or the level is sufficient to allow the user access to high enough sound levels, but risk overexposure due to potential duration of use.
Recent studies indicate that prolonged headphone listening at high volumes can cause Hearing Damage. Several cases have been documented, some even spawning lawsuits. Although Hearing Damage due to industrial noise exposure is more thoroughly understood, the risks associated with listening to headphones have also been studied. Researchers have attempted to determine headphone listening level recommendations based on experiments and accepted standards (Fligor and Cox, 2004).
However, no conventional art system monitors the SPL Dosage that is a combination of the attenuated ambient audio signal (passing through an earpiece) and the audio signal produced by an ear canal receiver, and compares the SPL dosage to an unprotected ear, and notifies a user when the earpiece should be switched to the other ear to minimize hearing damage to an unprotected ear.